- Child Parent bones are attached to objects on both sides of mirror? How to fix to only apply to one side?
Simply, your vertex groups (which attatch the armature) are copying to the other side of the mesh, so both the left and right arm are in the same group: The mirror mesh modifier, as far as I remember at the moment, does not automatically split and mirror vertex groups. Check that the "vertex groups" option is checked, and if it is, this is a bug.